Gasketing materials are commonly used to seal mating parts against fluid leaks. As examples, gaskets are frequently used between sections of conduits, such as in conduits for steam or air, and in automotive parts, such as in carburetors, manifolds, and cylinder heads. Not only must gaskets perform a primary function of sealing, they preferably should not stick to the parts against which they bear and, additionally, should have a relatively long service life.
In those cases where a laminated gasket is used and exposed to liquids, there is a further problem of resisting delamination. This problem is pecularily accentuated in cylinder head gaskets where the gasketing material is constantly exposed to circulation of a coolant, principally water. Such a coolant normally contains a number of chemical additives, such as rust inhibitors, like the chromates. Paradoxically, however, many of the added chemicals like rust inhibitors attack a gasket and particularly weaken the adherence of plies of a laminated gasket, thereby causing delamination.
In many instances, a gasket has by design a passage or metering hole through which a coolant is intended to pass, or the gasket may block the flow of coolant altogether. This results in added exposure to wear and can hasten the delamination of a gasket. In any case, a coolant tends in time to penetrate into the gasket and, where a metal core is present, corrode the core. This further weakens the adhesion line at the interface between the metal core and gasket facing, resulting in blistering which then accelerates delamination. There have been instances when parts of a gasket break loose and enter the coolant circulating system.
Cork is one material often used for making gaskets. While cork is compressible and relatively unaffected by oils, greases, gasoline, water, ethylene glycol, and such other liquids which it comes in contact in an internal combustion engine, cork is quite fragile and difficult to handle when setting a gasket in place as on an engine block. Further, when once compressed, cork tends to retain a permanent set and does not return to its original shape when a compressing pressure is released. As a result, cork gaskets are seldom reused and must be entirely replaced whenever disassembly of the engine block or other component is necessary.
Gasket facing materials in the automotive and truck industry are generally asbestos sheet materials bonded with a rubber binder. These materials are not waterproof and, as a result, have a high capacity for absorbing water, oil, coolants, and the like. This adsorption causes degradation of the facing, resulting in softening, loss of strength, and loss of adhesion between the facing and the core carrier of the gasket which is usually metal.
While some resinous materials have fluid resistance which adapt them to form a fluid barrier, they are not practical for gasket application, because they stick to metal under heat and pressure. Also, such resins are so smooth that it is most difficult to apply a uniform anti-stick coating over them. Often the parts joined about a gasket having a fluid barrier of this type cannot be disassembled without destroying the gasket. Also the gasket may stick so tightly to a part that it must be pried or chiseled away which inadvertently can damage the mating surface of such a part. This requires either a refinishing operation on the surface or an entire replacement of the part affected.
U.S. Pat. No. 2,025,486 to Victor discloses an impregnant for a gasket comprising aluminum sterate partially decomposed to a gummy consistency in solution with benzol and carbon tetrachloride with a suitable thinner.
U.S. Pat. No. 2,040,348 to Victor et al describes a saturant for an asbestos gasket comprising a composition resulting from a mixture of drying vegetable oils, such as China wood oil, linseed oil, turpentine, and metallic resinates.
U.S. Pat. No. 3,738,558 to Colwell discloses a thin gasket for high compression engines comprising two outer metal sheets and a compressible filler which may comprise fibers impregnated with a binder.
U.S. Pat. No. 3,970,322 to Stecher et al describes a cylinder head gasket for internal combustion engines comprising at least one layer of a soft material having pores which are enriched with an impregnating agent and edges which are bordered by a casing. The pores of the soft material underneath a flange are kept free of the impregnating agent.
The patents mentioned herein are hereby incorporated by reference.